Truck tires are commonly mounted on rims having two or more parts. During the mounting and inflation of truck tires on multiple part rims, it is possible that the lock ring and/or other parts of the rim, may become separated from the tire-rim assembly, causing the bead of the tire to become unseated from the rim and thus a sudden release of pressurized air from within the tire. This released air pressure can be extremely high and can cause the separated rim parts to be projected away from the assembly with considerable speed and force. When this happens, the rim is said to "explode". In order to protect persons and property in the event of such a rim explosion, safety devices or cages are used to restrain the multiple part rim during the inflation of truck tires. These cages must be capable of withstanding the large forces produced by the impact of flying rim parts. As a result, most of the cages are heavy and not readily moved.
In many instances, however, it is desired to mount and inflate a truck tire in the field. For example, when a tire is repaired and must be reinflated, such reinflations may occur on the highway or elsewhere away from the location of a conventional tire cage. It is often difficult or impossible to move the heavy tire cages to a field location. As a result, it is usually necessary to take the rim and tire to an installation where the cage is available to inflate the tire.
Several safety cages have been designed for use in the field which are collapsible and of relatively light weight so they can be stored conveniently on a service vehicle. U.S. Pat. No. 4,479,522, assigned to The General Tire & Rubber Company, discloses a design of and a portable safety cage. The cage has a base of two elongated tubular members, designed to rest horizontally on the ground, a vertical shaft connected to the midportion of the base, and a removable top retainer also made of tubular members. The top retainer slides onto the vertical shaft with opposite end portions extending over the top of a tire and rim combination sitting on the base. These basic design elements also exist in a prior portable safety cage sold by Myers Tire Supply Company of Akron, Ohio, but the design of the cage shown in the '522 patent includes a structural modification to the top retainer member, an inner support member designed to fit within the tire rim, and a means for maintaining the top retainer at a position rotated 90.degree. from the bottom retainer. In testing the cage, these modifications proved successful in preventing severe distortions to the base and retainer portions of the cage and thus eliminated the major cause of the lock-ring of the multiple piece rim escaping. However, because of the narrow, elongated shape of the top retainer member, the lock-ring was still prone to extreme bending about this retainer member and in some tests was able to free itself from the cage, although at a lower velocity than with cages of previous designs.
A possible solution to containing the lock ring better might be to make the top retainer member wider or to make it fan out in other directions over the top of the tire. However, this would add to the weight of the cage and reduce its collapsibility. Thus, it would be more difficult to transport and store the device.
The safety cage sold by Myers Tire Supply Company and another safety cage manufactured by Ken-Tool Division of Warren Tool Corporation, and the problems experienced with these cages are discussed in detail in the above mentioned U.S. Pat. No. 4,479,522.